The present invention relates to a semiconductor device and a method of fabricating the same.
Recently, the film thickness of a gate insulating film decreases as downsizing of MOSFETs advances, and this poses the problem that a gate leakage current increases. To suppress this gate leakage current, therefore, it is proposed to use a high-k film having a relative dielectric constant higher than that of a silicon oxide (SiO2) film as a gate insulating film. An example of this high-k film is a hafnium silicate nitride (HfSiON) film.
When a complementary MOS transistor (to be referred to as a CMOSFET hereinafter) including a PMOSFET and NMOSFET is to be formed, however, if this hafnium silicate nitride (HfSiON) film is used as a gate insulating film, the gate threshold voltage of the PMOSFET fluctuates more than that of the NMOSFET.
In this case, a driving current flowing through a channel region reduces more in the PMOSFET than in the NMOSFET, so the drivability of the PMOSFET decreases. This produces a large difference in drivability between the PMOSFET and NMOSFET.
A reference related to a CMOSFET using a high-k gate insulating film is as follows.
Japanese Patent Laid-Open No. 2004-289061